A silica glass crucible is used in the manufacture of a silicon single crystal. In a Czochralski (CZ) method, polysilicon is charged into a silica glass crucible, heated and melted and a seed crystal is immersed in this silicon melt, and while mutually rotating the crucible and the seed crystal, the seed crystal is slowly pulled up and a silicon single crystal is grown. In order to manufacture a high purity silicon single crystal for use in semiconductor devices, it is necessary that the silicon single crystal not be polluted by an elution of impurities which are included within the silica glass crucible and in addition, the silica glass crucible requires sufficient heat resistance strength.
The weight of the silicon which is charged into a crucible is increasing due to the large scale of silicon ingots in recent years. As a result, it becomes more difficult to remove gas bubbles which are included within the silicon melt and these gas bubbles are incorporated into the silicon single crystal during growth causing void defects (also called air pockets) which are formed within the crystal. Such problems have become noticeable. Argon (Ar) gas which is attached to the inner surface of the silica glass crucible, and silicon monoxide (SiO) gas which is produced by a reaction between the silica glass crucible and silicon melt are known as causes of the void defects. The void defects caused by gas bubbles largely have a spherical shape with a diameter of 300-500 μm taking up the majority of its size. However, very small void defects with a diameter of 150 μm or less and very large void defects with a diameter of 1 mm or more are also sometimes formed. In this way, void defects caused by gas bubbles clearly have different characteristics to Grown-in defects such as COP (Crystal Originated Particle). Presently, the presence of these defects can not be nondestructively inspected. The void defects can be detected only after a wafer has been cut from the ingot and appear as through holes or pinholes on the surface or interior section of the wafer.
In order to solves this problem, a method of adjusting a furnace pressure when melting polysilicon is proposed, for example, in Japanese Patent Application Laid Open Nos. H05-9097 and 2000-169287. In addition, a method of providing vibration to a crucible and starting growth of a silicon single crystal after reducing gas bubbles which are attached to the inner surface of the crucible is proposed in Japanese Patent Application Laid Open No. 2007-210803.
In recent years, the effects on semiconductor devices by pinholes with a wafer are extremely large. The effects of pinholes differ depending on the size, number, position of generation and type of semiconductor device. However, because pinholes are very large compared to COP, device can not be formed at all in spaces where pinholes exist. In particular, because yield of the semiconductor device decreases significantly when the number of pinholes within a wafer is large, the wafer itself has to be discarded. Therefore, it is necessary to reduce the possibility of pinholes being included within a wafer to almost zero.
However, gas bubbles can not be sufficiently removed by simply setting the furnace pressure when melting polysilicon higher or lower than when pulling up a silicon single crystal and thus a better method for sufficiently removing these gas bubbles is required.